1. Field of the Invention
The present invention relates to an electrochromic device and a production method thereof.
2. Description of the Related Art
A phenomenon that an oxidation and reduction reaction is reversely carried out to reversely change a color as voltage is applied is called electrochromism. A device utilizing this electrochromism is an electrochromic device. Various researches have been conducted on an electrochromic device to realize an application derived from properties of electrochromism.
As for an electrochromic material used for the electrochromic device, there are an organic material and an inorganic material. The organic materials can be colored in a various colors depending on the molecular structures thereof, and therefore the organic materials are promising materials to be used in a color display device. On the other hand, the inorganic material has a problem in controlling a color. In the case where a solid electrolyte layer is used, particularly, the inorganic material excels in durability. Therefore, application of the inorganic material in a light control glass or ND filter, which is an application where a low chromaticity is an advantage, has been studied using the aforementioned characteristics. However, a device using a solid electrolyte layer has a problem that a response speed is slow.
The electrochromic device has a structure where an electrochromic material is formed between two electrodes facing to each other, and the space between the electrodes is filled with an electrolyte capable of ion conduction. In this structure, an oxidation and reduction reaction is carried out. Electrochromism is an electrochemical phenomenon, hence a performance (ion conductivity) of the electrolyte layer affects a response speed or a memory effect of color. In the case where the electrolyte layer is in a liquid state where an electrolyte is dissolved in a solvent, a desired response tends to be attained. However, an improvement thereof by solidification or gelation has been studied in view of strength of an element, and reliability.
Conventionally, an electrolytic solution has been used in a battery or electrochromic device as an electrochemical element. Therefore, the electrolytic solution is leaked, and the contents inside the battery are dried due to evaporation of the solvent. Inside the battery container, moreover, part of the barrier is dried due to deviation of the electrolytic solution. These factors may cause an increase in internal impedance, and internal short circuit.
Especially in the case where the electrochromic device is used as a light control glass or a display, at least one side of the electrochromic device needs to be sealed with a transparent material, such as glass, or a plastic. Therefore, it is difficult to completely seal the electrolyte with a metal or the like, hence leak or evaporation of the electrolytic solution is a sever problem.
As for a method for solving the aforementioned problems, use of a polymer solid electrolyte is proposed. Examples of the polymer solid electrolyte include a solid solution between a matrix polymer containing an oxyethylene chain or an oxypropylene chain, and an inorganic salt. These solid solutions are complete solids, and they have excellent processability, but having a problem in electric conductivity.
In order to improve electric conductivity of the polymer solid electrolyte, proposed are a method where an organic electrolytic solution is dissolved in a polymer to formed into a semi-solid (see, for example, Japanese Patent Application Publication (JP-B) No. 03-73081), and a method where a liquid monomer to which an electrolyte is added, and the liquid monomer is reacted through a polymerization reaction to thereby form a crosslinked polymer containing the electrolyte. However, these proposed methods have not yet reached the level of practical use.
Meanwhile, the electrochromic device is typically produced by forming an electrochromic material between two electrodes facing each other, followed by bonding via an electrolyte layer capable of ion conduction. If the electrochromic device can be produced without this bonding process, the device can be formed on a various sites, such as a curved surface, hence an applicable ranges is widen, and the electrochromic device can be produced at a low cost, as a support of one side is not necessary.
In a conventional art, however, it has been difficult to form an electrochromic device on a support in accordance with a thin film process. Specifically, in the case where an electrode is formed on an electrolyte layer in order to omit the bonding process, there is the aforementioned problem that a response speed is slow, as an all solid electrolyte layer is used. If an organic material layer is used as an all solid electrolyte layer, moreover, electric resistance of an electrode layer to be formed on an electrolyte layer tends to be high, and the electrochromic device cannot be regularly driven with oxidation reduction. Particularly when an oxide layer, such as ITO, SnO2, and AZO formed by vacuum film formation, which are typically adapted as a transparent electrode, there is a problem that it is difficult to achieve transparency and electric conductivity at the same time.
In the case where an inorganic material layer is used as an all solid electrolyte layer, on the other hand, an electrochromic compound for use is limited to an inorganic electrochromic compound. Examples where the inorganic electrochromic compound is used include an electrochromic element having a structure, in which a reduction coloring layer and an oxidation coloring layer are provided to face each other with a solid electrolyte layer being in between.
In the electrochromic element, the reduction coloring layer is composed of a material containing tungsten oxide and titanium oxide, and the oxide coloring layer is composed of a material containing nickel oxide. Moreover, propose is an electrochromic element, in which a transparent intermediate layer that is composed of metal oxide other than nickel oxide, or a metal, or a complex containing metal oxide other than nickel oxide and a metal as a main component is provided between the oxide coloring layer and a solid electrolyte layer (see, for example, is Japanese Patent (JP-B) No. 4105537). This literature discloses that repetition properties and response are improved by forming the intermediate layer, hence coloring-discharging can be performed within a few seconds.
However, this proposed electrochromic element has a complicated structure, and cannot be easily increased in its side, as multiple layers of the inorganic compound layer are formed by vacuum film formation, as well as increasing a cost. Moreover, it cannot avoid an influence from heat during the film formation process, and therefore the substrate for use is limited to a heat resistant material, such as glass. Furthermore, the inorganic electrochromic reaction is easily influenced by moisture, and a color tone of the inorganic electrochromic compound is limited to a tone of blue.
Accordingly, there is a need for promptly providing an electrochromic device which can be produced without a bonding process.